A cavity-backed annular slot (CBAS) antenna typically includes a metal surface having a radiating element and an annular slot through which electromagnetic energy is radiated. The metal surface is backed by a resonant cavity that encloses an antenna feed structure for providing excitation to the radiating element. These CBAS antennas provide an omnidirectional azimuth gain pattern, which enables efficient reception and transmission between transmitters and receivers that are positioned in the same plane as the antenna.
The structure and gain pattern of the CBAS antenna enables it to be used as a conformal antenna. That is, CBAS antennas are often used in antenna applications that require the antenna to be conformal to an external surface so that the antenna or any protruding elements of the antenna do not interfere with the desired characteristics of the external surface. For example, a CBAS antenna may be integrated into a flat or curved external surface of a vehicle (e.g., aircraft, watercraft, spacecraft, or land vehicle) to prevent or reduce aerodynamic drag or any other adverse effects to the aerodynamics of the vehicle surface.